The invention relates to a linear motor, and in particular a canned linear motor, used for, for example, feeding in electronic component inspection apparatuses and machine tools, etc., in which an increase in temperature is suppressed and constant-rate feeding accuracy is required.
In a canned linear motor provided with three-phase armature winding at its stator and a permanent magnet, used as a field system, at its mover, the armature winding is directly cooled by a coolant, wherein an increase in the surface temperature of the linear motor can be suppressed to be low.
However, according to the conventional art, since there is completely no problem if a structure in which a mover and a stator are replaced with each other is employed, such a type in which the mover is provided with armature winding has been frequently used in applications where the stroke is long.
Herein, a description will be given mainly of a canned linear motor in which an armature winding formed of a plurality of coil groups is made into a mover, and a plurality of permanent magnets of which used field systems, which have different polarities from each other are juxtaposed adjacent to a stator. However, the canned linear motor is not limited to this specification.
FIG. 8 is a perspective view showing the entirety of a linear motor in a conventional art. In FIG. 8, reference number 80 denotes a mover, reference number 81 denotes a mover base, reference number 84 denotes a can, reference number 31 denotes a coolant discharge port, reference number 32 denotes a coolant supply port, reference number 33 denotes a cable, reference number 90 denotes a stator, reference number 91 denotes a stator base, reference number 92 denotes a field system yoke, and reference number 93 denotes a permanent magnet.
The mover 80 is formed to be T-shaped as described later, wherein its longitudinal member (armature) is supported by a linear guide, an air slider, and a slider guide, etc., between the permanent magnets 93 disposed between the field system yokes 92 and 92 of the stator 90, and by causing an appointed current to flow into the armature winding, the longitudinal member operates with a magnetic field produced by the permanent magnets 93 to generate a thrust in the mover 80, by which the motor 80 is movable in the directions of travel shown by the arrows.
FIG. 1(b) is a cross-sectional view of a conventional art linear motor of FIG. 8 when observing the same from the front side thereof. In the drawing, the mover 80 is formed to be T-shaped. The mover 80 is composed of a mover base 81, a can 84 supported in a depression of the mover base 81 downward, a header 84xe2x80x2 (See FIG. 5) to seal the can 84, a winding fixing frame 82 disposed in a gap produced by the can 84 and the header 84xe2x80x2, a coreless type three-phase armature winding 83, which is fixed at the winding fixing frame 82, and a coolant passage 87 passing through the can 84.
FIG. 5(a) shows a side elevational view of the mover, and FIG. 6 shows a view of arranging an armature winding when being observed from the mover side. Herein, as shown in FIG. 6, the armature winding 83 is formed of three phases and is thin plate-shaped. By adhering the same to both the right and left sides of the winding fixed frame 82, the entirety of the armature winding is constructed, and the strength thereof is improved. Also, since the winding fixing frame 82 itself needs strength, the winding fixing frame 82 is frequently made of stainless steel.
The can 84 is rectangular-tubular, for which a stainless steel thin plate is bent to be channel-shaped and welded together. Two headers 84xe2x80x2 (FIG. 5) made of stainless steel casting are provided with a coolant supply port 32 and a coolant discharge port 31, through which a coolant is permitted to pass. The can 84 and headers 84xe2x80x2 are welded together at the conjunction plane.
Also, by causing a coolant to be supplied through the coolant supply port 32 and to be discharged through the coolant discharge port 31, the coolant flows through a coolant passage 87 (FIG. 1(b)) located between the armature winding 83 and the can 84.
On the other hand, as shown in FIG. 1(b), the stator 90 is recess-shaped so that it can wrap the armature portion of the mover 80. The stator 90 is composed of a permanent magnet 93 disposed at both sides of the can 84 and header 84xe2x80x2 of the mover 80 with a gap, a field system yoke 92 made of a magnetic body that causes a magnetic flux produced by the permanent magnet 93 to pass through, and a stator base 91 to support the same. Also, a plurality of permanent magnets 93 juxtaposed in the direction of travel are disposed so that the same have a different polarity from each other at each polarity pitch xcex (FIG. 8).
The canned linear motor thus constructed operates with a magnetic field produced by the permanent magnet of the stator by causing an appointed current appropriate to a position of the mover to flow into the armature winding, wherein a thrust is generated at the mover, and the armature winding heated due to a copper loss is cooled by the coolant, and a temperature rise at the surface of the mover can be suppressed to be low.
However, in the conventional art, there are the following problems.
The can 84, winding fixing frame 82, header 84xe2x80x2, etc., are made of stainless steel as described above. The members made of stainless steel materials generate an eddy current ie at each polarity pitch xcex by passing between the permanent magnets 93 of the stator 90. FIG. 5(b) shows a view of an occurrence of the eddy current ie. As has been made clear in FIG. 5(b), the eddy current ie of the conventional art device flows, depicting a large loop, so that the flow passage extends entirely in the vertical direction of the can 84 and header 84xe2x80x2. And, a viscous damping force is generated by vertical direction constituents of the eddy current ie. The viscous damping force crosses the magnetic flux produced by the eddy current ie and permanent magnet 93 and is generated in a reverse direction of the direction of travel of the mover 80. The intensity thereof is almost proportionate to the thickness and width of stainless steel, travel speed of the mover 80, number of points where the eddy current ie occurs, and square of the magnetic flux density. The following problems further occur due to generation of such a viscous damping force.
(1) Where a certain thrust is attempted to be gained, the thrust is decreased equivalent to the size of the viscous damping force even if an appointed armature current is caused to flow, wherein it becomes necessary to cause a greater armature current to flow than is usually necessary. Resultantly, the copper loss of the armature winding is increased, temperature of the can and the surface of the header is accordingly increased.
(2) The eddy current is converted to heat as a so-called eddy current loss at a point where an eddy current is generated. That is, the can, winding fixing frame and header where the eddy current is generated are heated, resulting in a further rise in temperature. In applications where the temperature is remarkably limited, there may be a case where no expected specification can be satisfied by the heating.
(3) Recently, a viscous damping force has tended to be further increased in line with a request for increasing the speed, and further the viscous damping force is generated in a reverse direction of the travel direction of the mover, wherein the speed of a linear motor is subjected to fluctuations due to fluctuations of the viscous damping force. Since influences of the viscous damping force onto fluctuations in the speed of the linear motor are comparatively slight in comparison with a thrust generated, the influences are not highly emphasized. However, in recent years, requests to decrease fluctuations in the speed have increased in line with recent needs for high accuracy and high density in various types of precious machines and apparatuses, etc. Therefore, it has been required that, without changing the materials of components, fluctuations in the speed of a linear motor are suppressed and decreased while suppressing the fluctuations in the viscous damping force with mechanical strength maintained.
The invention was developed in order to solve these and other problems, and it is therefore an object of the invention to provide a canned linear motor that is capable of suppressing a rise in the temperature of the mover, decreasing the viscous damping force, and suppressing the ratio of fluctuations, and in which the strength of the can does not deteriorate.
In order to solve the above-described problems, a canned linear motor according to the first aspect of the invention is featured in that the canned linear motor includes field system yokes, having different polarities from each other, in which a plurality of permanent magnets are juxtaposed adjacent to each other; an armature disposed so as to be opposed to the above-described permanent magnet row with a magnetic gap secured therebetween and having an armature winding; in which the above-described armature is provided with a winding fixing frame having the above-described armature winding mounted on both sides thereof along the lengthwise direction of the above-described armature; a can that accommodates the above-described armature winding and the above-described winding fixing frame and has a coolant passage for causing a coolant to flow to the periphery of both the members; and a header having a coolant supply port attached at one of both ends of the above-described can and having a coolant discharge port attached at the other end thereof; and in which any one of the above-described field system yokes and the above-described armature is made into a stator, and the other of which is made into a mover, and the above-described field system yokes and the above-described armature are caused to run relative to each other; wherein a plurality of slits are provided in the above-described can, a leak preventing sheet is adhered to the inside of the above-described can so as to cover the above-described slits; and at the same time, resin is filled in the above-described slits.
Further, a canned linear motor according to the second aspect of the invention is featured in that, in addition to the canned linear motor described in the first aspect of the invention, the above-described plurality of slits extend in the direction of travel in parallel to each other.
Also, a canned linear motor according to the third aspect of the invention is featured in that, in addition to the canned linear motor described in the first aspect of the invention, the above-described plurality of slits are split in parallel to each other and in the direction of travel.
In addition, a canned linear motor according to the fourth aspect of the invention is featured in that, in addition to the canned linear motor described in the first or third aspect of the invention, the above-described plurality of slits are disposed one by one every 3xc3x97xcex (xcex=polarity pitch).
Also, a canned linear motor according to the fifth aspect of the invention is featured in that, in addition to the canned linear motor described in the first, third or fourth aspect of the invention, the above-described plurality of slits are split in parallel to each other and in the direction of travel, and a deviation of 1.5xc3x97xcex (xcex=polarity pitch) is provided between the above-described slits and adjacent slits in the direction orthogonal to the direction of travel.
Further, a canned linear motor according to the sixth aspect of the invention is featured in that, in addition to the canned linear motor described in any one of the first through the fifth aspects of the invention, the above-described header is provided with a plurality of slits extending in parallel to each other in the travel direction, and a leak preventing sheet is adhered to the inside of the above-described header so as to cover the above-described slits, and at the same time, resin is filled in the above-described slits.
And, a canned linear motor according to the seventh aspect of the invention is featured in that, in addition to the canned linear motor described in any one of the first through the six aspects of the invention, the above-described winding fixing frame is provided with slits extending in parallel to each other.
Further, a canned linear motor according to the eighth aspect of the invention is featured in that the canned linear motor includes field system yokes, having different polarities from each other, in which a plurality of permanent magnets are juxtaposed adjacent to each other; an armature disposed so as to be opposed to the above-described permanent magnet row with a magnetic gap secured therebetween and having an armature winding; in which the above-described armature is provided with a winding fixing frame having the above-described armature winding mounted on both sides thereof along the lengthwise direction of the above-described armature; a can that accommodates the above-described armature winding and the above-described winding fixing frame and has a coolant passage for causing a coolant to flow to the periphery of both the members; and a header having a coolant supply port attached at any one of the both ends of the above-described can and having a coolant discharge port attached at the other end thereof; and in which the above-described field system yokes are made into a stator and the above-described armature winding is made into a mover, and the above-described field system yokes and the above-described armature are caused to run relative to each other; wherein the entire length L of the above-described can is defined as follows:
L=(n+1/2)xcex
where L is the entire length of the can, xcex is a polarity pitch of the permanent magnets, and an integer is n.
With the above-described construction, since the number of points where an eddy current occurs is made constant, and fluctuations of a viscous damping force are remarkably suppressed, it becomes possible to reduce fluctuations in the speed of a linear motor.